In the field of orthopedic surgery it is common to rejoin broken bones. The success of the surgical procedure often depends on the ability to re-approximate the bone fragments, the amount of compression achieved between the bone fragments, and the ability to sustain that compression over a period of time. If the surgeon is unable to bring the bone fragments into close contact, a gap will exist between the bone fragments and the bone tissue will need to fill that gap before complete healing can take place. Furthermore, gaps between bone fragments that are too large allow motion to occur between the bone fragments, disrupting the healing tissue and thus slowing the healing process. Optimal healing requires that the bone fragments be in close contact with each other, and for a compressive load to be applied and maintained between the bone fragments. Compressive strain between bone fragments has been found to accelerate the healing process in accordance with Wolf's Law.
Broken bones can be rejoined using staples. Staples are formed from a plurality of legs (typically two legs, although sometimes more) connected together by a bridge. Staples are typically manufactured from stainless steel alloys, titanium alloys or Nitinol, a shape memory alloy. The legs of the staples are inserted into pre-drilled holes on either side of the fracture line, with the bridge of the staple spanning the fracture line.
Existing staples need to be impacted so as to make the bottom of the staple bridge sit flush with the bone surface following implantation of the staple legs into the pre-drilled holes. This is because current staples and their associated delivery devices are typically designed to grip the staples under the bridge of the staple. After the staple has been deployed from the delivery device, there is a gap between the bottom of the bridge and the top surface of the bone. A tamp is typically used to fully seat the staple bridge against the bone surface. Thus, an additional step (i.e., the tamping step) is required. In addition, the action of tamping can cause the bone fragments to move out of position, impairing healing.
Furthermore, current staple systems do not allow the surgeon to control the amount of compression that the staple will exert when it is released from the delivery device. While the shape memory and superelastic properties allow Nitinol staples to pull together the opposing bone fragments, the recovery forces and recoverable strain generated by these staples may be too great and may result in the staples “tearing through” the bone tissue and thus not providing a means to generate and maintain compression between the bone fragments.
Additionally, current staple systems do not allow the surgeon to control the rate at which the staple loads the bone when it is removed from the delivery device. Current delivery devices load the bone nearly instantaneously. This may result in a large force impulse as the staple's legs rapidly undergo shape recovery. This force impulse may damage the bone and result in impaired healing.
Current staple systems also do not allow the surgeon to control the extent to which the staple's legs are opened. This can make it particularly difficult to implant the staple into the pre-drilled holes if the holes were drilled slightly out of position. More particularly, if the pre-drilled holes are slightly too close together or slightly too far apart, it may be difficult to fit the staple legs into the holes and may result in impaired healing.
Finally, current staple systems do not allow for the staple to be easily removed following implantation. Since the staples are tamped flush with the bone surface, there is no easy way for surgeons to grip and remove current staples. It is very time-consuming for surgeons to pry out deployed staples and it is difficult to cut deployed staples for removal. In addition, these actions may damage the underlying bone, thus impairing healing and may result in the patient needing to be under anesthesia for a longer period of time.
Thus there exists a significant clinical need for a new staple and a new associated delivery device to implant the staple flush with the bone surface without the need for tamping to fully seat the staple. Additionally, there is a significant clinical need for a staple system that allows the surgeon to control the amount of compression the staple will generate across the fracture line after the staple has been implanted into bone, to control the rate at which the staple loads the bone, to allow the surgeon to adjust opening the staple legs for proper alignment with pre-drilled holes, and to allow the staple to be easily removed from the bone if desired.